The present invention relates generally to aircraft engines, and, more specifically, to thrust reversers therein.
Turbofan engines are typically composed of a fan driven at the front of the engine that draws air through a bypass duct that is bounded by the engine cowling on the inner surface and by the fan cowling on the outer surface. In the case of a short nacelle, the generally annular duct that is bounded by the inner cowling and the outer cowling channels the bypass flow only, while in the case of a long nacelle, the upstream portion of the annular duct channels the bypass flow only, and its downstream portion channels both the bypass flow and the engine core flow.
Thrust reversers for turbofan type engines are well known in the art. The nacelle of the turbofan engine on which the thrust reverser can be installed can be long or short. The engine of the aircraft can be installed under the wing or on the fuselage. The thrust reverser can be installed on commercial or business aircraft.
The known prior art fan thrust reversers can be, generally speaking, categorized in three distinct types. The first type effects aft axial translation of the bypass structure for deployment of a series of blocker doors inside the bypass duct structure and the opening of an aperture in conjunction with exposing of radial cascade vanes for redirecting the bypass flow in the forward direction.
The second type also effects aft axial translation of the bypass structure for closing the bypass flow duct and opening an aperture for redirecting the bypass flow in the forward direction. The aperture of the prior art may or may not be equipped with cascades vanes. The second type differs from the first type as the series of blocker doors is no longer present.
The third type includes doors that rotate inside the bypass flow and outside in the ambient air for redirecting the bypass flow in the forward direction. This fan reverser type is generally called petal or pivoting door reverser.
The drawbacks of the first type prior art fan reversers are the necessity to provide aft translation capability to the rear portion of the bypass duct for reversing the fan flow, and the presence in the bypass duct of links, known as drag links, for the deployment of the series of blocker doors. The drag links degrade engine performance in forward thrust, while the required guiding and sliding tracks of the translating cowls increase weight of the nacelle.
While the second type of fan reverser appears to be an improvement, since the drag links and the associated series of blocker doors have been eliminated, its drawback is that it necessitates the provision of a large bulge on the cowling of the engine so that the structure of the bypass duct that translates rearward can block the bypass flow for reverse flow purposes.
Although the third type appears to be an improvement over the first and second types, its main drawback is the presence of wells in the bypass duct for housing the actuators that control pivoting of the doors. The forward engine performance degradation that is associated with these wells usually requires an additional flap mechanism for fairing them. Other drawbacks of this type of fan reverser are the required large actuator stroke and the extensive protrusion of the pivoting doors in the ambient air when they are pivoted to their deployed position.
During thrust reverse operation, the doors are driven from their flush and stowed position to their deployed and rotated position. The deployed doors may thusly engage the aft-flowing ambient freestream air, and the aft-flowing engine exhaust flow for redirecting it forward to provide aircraft braking thrust.
Since the freestream air and exhaust flow exert aerodynamic pressure loads on the deployed doors which act in the direction of deployment, redundant latching systems are typically used to prevent inadvertent deployment of the doors. Such latching systems add complexity, weight, and expense to the thrust reverser system.
Accordingly, it is desired to provide an improved fan thrust reverser which is self contained in the fan nacelle for reducing size, complexity, weight, and drag.
More specifically, a first object of the thrust reverser is to provide a self-stowing feature.
A second object of the thrust reverser is to provide thrust reverse in a turbofan engine that does not require aft translation of any portion of the bypass duct.
A third object of the reverser is to eliminate drag links in the bypass duct when the reverser is in its forward thrust position.
A fourth object of the reverser is to provide for optimum direct thrust performance of the engine, and a clean aerodynamic boundary flow surface for the outer cowling of the bypass duct.
A fifth object of the reverser is to eliminate the series of cascades.
A sixth object of the reverser is to limit the amount of external protrusion in the ambient air of the thrust reverser structure when in the deployed position.
A seventh object of the reverser is to reduce the stroke of the deployment actuators for further weight reduction.